Chaotic Behavior in Ytterbium Nuclei*

We describe a new method to study the order-to-chaos transition in rotational Yb nuclei. Correlations between successive (unresolved) gamma rays are used to determine the average complexity of the intermediate levels and thereby the average ratio, v/d, of the interaction potential between levels to the level spacing. The measured ratios, 0.15 to 1.5, span the range from nearly fully ordered to nearly fully chaotic [1]. We will also describe a new project to measure the spreading width, the energy region over which a given level is mixed. Together with v/d (which measures the amplitude remaining in the initial state), this would allow us to determine v and d separately. [1] F.S. Stephens et al., Phys. Rev. Lett., in press.